Gas turbine arrangements are widely utilized for the production of electrical power. Such arrangements generally involve: a compressor, which takes ambient air and compresses it to about 15-20 bar, increasing the temperature to about 600-700.degree. F. (315-371.degree. C.); a burner, through which the compressed air passes, which increases the temperature of the gases to at least about 2000-2200.degree. F. (1080-1190.degree. C.); and, an expander, in which the gases are expanded to about ambient pressure with a typical temperature reduction to about 1000.degree. F. (540.degree. C.). Energy released during the expansion process is used to drive a generator, for production of power.
Typical gas turbine arrangements are rated for percent of design output, percent of design air flow and percent of design heat rate, vs. compressor inlet temperature. This is exemplified in FIG. 1, which reflects such plots for a General Electric model MS7001 turbine, a gas turbine rated for 145,400 KW (145 megawatt) output at 100% design output.
Upon examination of FIG. 1, it will be understood that the gas turbine involved is rated for 100% design output at compressor inlet (air) temperatures of about 59.degree. F. (15.degree. C.). As the gas temperature (inlet temperature) increases above 59.degree. F. (15.degree. C.), output, i.e. energy production, drops off rapidly, for example to a figure of about 90% of the rated value at about 84.degree. F. (29.degree. C.), and only about 84% output at 100.degree. F. (38.degree. C.). On the other hand, energy production is favored by inlet air temperatures below 59.degree. F. (15.degree. C.). It is noted that there is a linear or nearly linear relationship between energy production, i.e. percent of design output, and compressor inlet air temperature, over the temperature range shown.
It is also noted that there is also a linear or nearly linear relationship between percent of design air flow, i.e. volume of air passing through the turbine for a given percent design output, and temperature of compressor inlet air. As the compressor inlet air temperature is increased, percent of design air flow decreases. Alternatively stated, output requires a decrease in air flow, as air temperature increases. A General Electric MS7001 is rated for an air flow of about 3,255,000 lb of air/hr at 100% design air flow.
Further, there is a linear or nearly linear relationship between percent of design heat rate, and compressor inlet air temperature. As the compressor inlet air temperature is increased, the percent of design heat rate increases. This figure can be directly related to the amount of fuel or energy needed in the burner, to appropriately increase the temperature of the gases, for use in the gas turbine. A plot of percent design heat consumption versus inlet temperature is also provided.
FIG. 1 exemplifies a well known and widely observed phenomenon in industries utilizing gas turbines for power production, the particular turbine presented merely being an example. The General Electric MS7001 turbine was selected, since it is one of the newest, most efficient, designs available. As with any conventional turbine, as the ambient temperature increases, power output from the arrangement decreases. This means that the power production for such systems can be expected to vary, seasonally, with wide swings in ambient air temperature. Efficiency is substantially decreased if the ambient air, channeled to the turbine inlet, is hot. In many instances as much as a 30% decrease in maximum of power production occurs just through a swing of ambient temperature from about 30.degree. to 90.degree. F. (-1.degree. to 32.degree. C.).